The present invention relates to a method for checking the plausibility of the measured load in an internal combustion engine having variable valve lift control.
Such a plausibility check is, for example, practical with torque monitoring in which an acceptable engine torque, which essentially results from the engine speed and the accelerator pedal position, is compared with an actual torque calculated from engine variables. As a rule, these engine variables include the ignition angle, the engine speed and the engine load. In order for the effectiveness of the torque monitoring not to be limited by continuously too little load information, the plausibility of the measured load signal should be checked with regard to an excessively low value. A comparison of load information obtained from the throttle valve position and the engine speed with the measured load is known for a conventional internal combustion engine from European Published Patent Application No. 0 778 406. If the measured load varies from the load information derived the throttle valve position and the engine speed by a specific amount, an incorrect load measurement is assumed and an error correction is initiated accordingly.
An object of the present invention is now to specify a method of the aforementioned type with which a measured load can also be checked for plausibility in an internal combustion engine having variable valve lift control.
The stated objective is attained in that an initial piece of load information is derived as a function of the throttle valve position and a differential pressure determined from the pressure upstream of the throttle valve and the pressure downstream of the throttle valve in the intake manifold. A second piece of load information is derived as a function of the intake valve lift and the engine speed. The smaller of the two pieces of load information is finally compared with the measured load and an error of the measured load is signaled if it deviates from the load information with which it is compared. With this method according to the present invention, it is taken into account that in addition to the throttle valve, the valve lift control also brings about a throttling effect.
For the event that the determined differential pressure or the intake valve lift is incorrect and thus no throttling is possible via the valves, it is advantageous to derive a third piece of load information as a function of the throttle valve position and the engine speed and then to make a comparison with the third piece of load information for a plausibility check of the measured load.
For a very reliable plausibility check of the measured load, it is advantageous to also check the determined differential pressure and the intake valve lift for plausibility. The plausibility check of the differential pressure is performed in such a way that differential pressure information is derived as a function of the throttle valve position and the engine speed, this information being compared with the determined differential pressure, and an error of the differential pressure is signaled if the determined differential pressure is less than the differential pressure information. The plausibility check of the intake valve lift can be performed in such a way that the second piece of load information derived from the intake valve lift and the engine speed is compared with the measured load or a load derived from the throttle valve position and the intake manifold differential pressure, and an error of the intake valve lift is signaled if the second piece of load information is less than the measured load or a load derived from the throttle valve position and the intake manifold differential pressure.
The first piece of load information is advantageously obtained in such a way that the air mass flow to the throttle valve is read out of an engine characteristics map as a function of the throttle valve position and the differential pressure and that this air mass flow is divided by the engine speed which is multiplied by an engine-specific factor which is a function of the number of cylinders and the piston displacement.
The second piece of load information is advantageously obtained in such a way the air mass flow through the intake valve(s) is read out of an engine characteristics map as a function of the intake valve lift and the engine speed and that this air mass flow is divided by the engine speed which is multiplied by an engine-specific factor which is a function of the number of cylinders and the piston displacement.